High voltage supply circuit for television systems



HIGH VOLTAGE SUPPLY CIRCUIT FOR TELEVISION SYSTEMS Filed 001;. 29, 1938 Invent or: Robert B. Dome,

His Attorney.

Patented Nov. 7, 1939 UNITED STATES HIGH VOLTAGE SUPPLY CIRCUIT FtOR TELEVISION SYSTEMS Robert B. Dome, Bridgeport, Gonm, assignor to General Electric Company, a corporation of New York Application October 29, 1938, Serial No. 237,785

Claims.

My invention relates to high voltage power supply circuits and particularly to power supply circuits for cathode-ray tubes used in television systems.

5 In television receivers power is required to be supplied to the cathode ray tube at a relatively high voltage. It has been suggested heretofore to supply this power by providing a special high voltage winding arranged to be energized by the usual transformer which supplies power to amplifier or other tubes of the system. The above arrangement, suggested heretofore, entails the disadvantage that this special winding is of relatively high cost.

It is an object of my invention to provide a high voltage power circuit for television cathode ray tubes which adds relatively little to the cost of the system.

It is a particular object of the invention to 20 utilize, for producing the high voltage power for the cathode ray tube, transformers of no higher voltage than those ordinarily available for pro- Viding power in usual radio broadcast receivers.

It is a further object of the invention to utilize 25 as a voltage source for the cathode-ray tube the secondary winding of the power transformer which supplies the usual amplifier or other tubes of the receiver.

It is another object of the invention to provide, for the energizing of the cathode-ray tube, a voltage which is the sum of the voltage produced as above describedbythe secondary winding of the above-mentioned power transformer and the voltage, including that due to the drop through a filter reactor, supplied to a circuit connected to the power transformer for the supply of power to the amplifier or other tubes of the system.

It is a still further object to provide a low cost filter system for the high voltage cathoderay tube supply circuit.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing wherein Fig. 1 is a diagrammatic representation of a portion of a television receiver in which my invention has been embodied, and Fig. 2 is a diagrammatic representation of a modification of the invention illustrated in Fig. l including an improved filter system for the cathode-ray power supply circuits.

(C11. Till-97) In Fig. 1 the television system illustrated therein includes a usual rectifier circuit for the supply of power for the operation of conventional radio receiver tubes. This usual supply circuit, designated generally by S1, comprises a transformer so having a primary it connected to a current source (not shown) and a secondary I2; a rectifler apparatus or tube i3 having anodes l4 and it connected to the opposite terminals l6 and ll of secondary t2 and a cathode l8 supplied with heating current from a secondary winding 09 of transformer ill; output terminals and 2| connected respectively to the cathode I8 and to the mid-tap 22 of secondary I 2; and. a filter means including a filter reactor 23 and capacitors 24 and 25.

In order to provide the high D. C. voltage required for the cathode-ray tube (not shown) and which is to be supplied thereto through the output terminals 26 and 21 of the cathode ray tube supply circuit, designated by S2, instead of providing on transformer ID a special winding designed to produce the required high cathode-ray tube voltage, I utilize the relatively high voltage winding 02 which is already provided on transformer ID and which is designed for-the supplying of voltage for the conventional radio receiver tubes (not shown), or for other purposes, through the output terminals 20 and 2|. For the purpose of utilizing winding l2 as a voltage source for the cathode ray tube supply circuit, an auxiliary rectifier tube 28 is provided having an anode 29, and a cathode 30 heated from a secondary winding 3| on transformer lfl. Rectifier 28 is supplied with alternating voltage from secondary winding l2 through a capacitor 32 connected between one terminal ll of winding l2 and the cathode 30 of tube 28, and through a capacitor 33 connected between the other terminal l6 of winding l2 and the anode of tube 28.

A filter capacitor 34 is connected across the cathode-ray tube supply circuit S2. Cathode 30 of auxiliary rectifier 28 is connected to the high voltage terminal 26 of the cathode-ray tube supply circuit through a connection including a resistor 35. The anode 29 of tube 28, however, instead of being connected to the other output terminal, H, of the cathode-ray tube circuit, is connected for a purpose to be described hereinafter to the cathode l8 of main rectifier [3 through a resistor 36 and the connection 37 between cathode l8 and filter reactor 23. In addition to the filtering provided in the cathode-ray tube supply circuit S2 by capacitor 34 and resistors and 36 an extra filter stage is preferably providedcomprising a filter resistor 38 and a capacitor 39. The high voltage for the cathoderay tube is thus taken off between the terminals of capacitor 39. A voltage divider 40 is prefer- 5 ably provided connected between the cathoderay tube supply circuit output terminals to permit the obtaining of additional voltages as for focus voltage for the cathode ray tube. 1

From the foregoing description of the system 1 illustrated in Fig. 1 it will be seenthat the radio receiver tube supply circuit, indicated generally by S1, may be readily traced from positive terminal 20, through reactor 23, main rectifier tube l3, secondary l2 of transformer l0, and mid-tap 22 of secondary I2, to terminal 2| which may be at ground. It will also be seen that the cathoderay tube supply circuit, indicated generally by S2, may be traced from the high voltage terminal 26, through resistor 38, resistor 35, auxiliary rectifier tube 28, resistor 36, filter reactor 23 of circuit S1, and the load between terminals 20 and 2| of circuit S1, to terminal 21.

In operation of the system illustrated in Fig. 1, let it be assumed that the cathode-ray tube supply circuit S2 is under no-load conditions, no current being drawn from the output terminal 26, and that the supply circuit S1 is under load conditions. Under these conditions twice the R. M. S. voltage per anode for the main rectifier I3 exists across the transformer secondary l2. The latter R. M. S. voltage is rectified by the auxiliary rectifier 28 and when, as assumed, no D. C. drain occurs from this tube since the circuit S2 is under no-load conditions, the voltage produced by rectification in rectifier 28 and appearing in the cathode-ray tube supply circuit S2 iS times the R. M. S. voltage across secondary l2.

Also, under the assumed conditions, a predetermined output voltage exists across terminals 20 and 2| of thesupply circuit S1, and a predetermined voltage drop due to the current drain in the supply circuit S1 exists across the filter reactor 23. A total predetermined voltage therefore exists across the capacitor 24 of circuit S1, this total voltage being'the sum of the load voltage across terminals 20 and '2| and the voltage drop across the filter reactor 23.

Since the anode 29 of auxiliary rectifier 28 is connected, through resistor 36 and connection 31, to the positive terminal, 4|, of filter reactor 23, therefore the above-noted sum of D. C. voltages across capacitor 24 of circuit S1 is added to the D. C. voltage produced from transformer secondary l2 by rectification in auxiliary rectifier 28. Therefore, under the assumed no-load conditions in cathode-ray tube supply circuit S2 and load conditions in receiver tube supply circuit S1, the total voltage appearing across -ter-- minals 26 and 21 of cathode-ray tube supply circuit S2 is the sum of 20 and 2| of supply circuit S1 is 265 volts and the load current drain from this circuit is 180 milliamperes. In filter reactor 23, five watts are consumed and the voltage drop across 23 is E=- =28 volts Therefore the sum of the voltages, in supply circuit S1, across capacitor 24 is 265+28=293 volts.

The R. M. S. voltage per anode in main rectifier I3 is approximately 315 volts and therefore the R. M. S. voltage across secondary I2 is 2 3l5=630 volts.

The rectifier voltage produced by auxiliary rectifier 28 under no-load conditions in circuit S2 is JE 630=890 volts D. c.

The total voltage at the output terminals 26 and 21 of the cathode-ray tube supply circuit S2 under no load conditions in the latter circuit is Ez=890+293 =1183 volts Under load conditions in circuit S2 the output current may be approximately 200 microamperes. This current flows through resistors 35, 36, and The total resistance of these resistors in order to obtain approximately 1000 volts across terminals and 21 of circuit S2 is .Parts 35 and 36 are 200,000 ohm, 1 watt re- R =915,000 ohms .sistors, and the resistance of resistor 38 is apbe noted that the only parts which would not be used in the system in accordance with my invention if the special secondary winding were provided are capacitor 33 and resistor 36. Capacitor 33 is, suitably, merely a 400 volt D. 0., onequarter microfarad paper condenser, ,as the ripple across it is negligible, and it is required to withstand only the D. C. voltage across capacitor 24 which is 293 volts. Resistor 36 merely withstands principally the A. C. voltage of onehalf of secondary i2, or 315 volts A. C. The loss in resistor 36 is therefore It will be readily seen therefore that the added parts 33 and 36 required in the above-described system in accordance with my invention are of relatively low cost and represent a very considerable saving as compared with the prior systems wherein the relatively expensive special high voltage secondary for transformer I0 is employed to supply the cathode-ray tube circuit.

In Fig. 2 is illustrated a television system identical in all respects with the system illustrated in Fig. 1 except that in Fig. 2 a filter means for the cathode-ray tube supply circuit S2 is provided which lowers still further the cost of the system in accordance with my invention as compared with the hereinbefore mentioned system of the prior art wherein a separate secondary winding is employed for the supply of high voltage power for the cathode ray tube. In Fig. 2 the filter stage comprising filter resistor 38 and capacitor 39 of Fig. 1 is dispensed with and filter capacitor =0.5 watt 34 of Fig. 1 is replaced by a smaller capacitor to be described hereinafter.

The filtering for circuit S2 in Fig. 2 is accomplished by means of a filter circuit comprising the smaller filter capacitor which is designated by the numeral 42 replacing capacitor 34 of Fig. 1; resistor 35 in series with capacitor 32 as in Fig. 1; and an added resistor 43 in series with an added capacitor 44. Filter capacitor 42 is connected between output terminal 26 of cathode ray tube supply circuit S2 and output terminal 20 of supply circuit S1. Capacitor 32 and resistor 35 are connected in series between terminal ill of secondary winding l2 and terminal 26 of circuit S2. Added resistor 43 and added capacitor 44 are connected in series between terminal it of secondary winding l2 and terminal 26 of circuit S2. Resistor 43 is substantially equal in resistance value to resistor 35 and capacitor 44 is substantially equal in capacitance value to capacitor 32.

The above described filtering means for the cathode-ray tube supply circuit S2 in Fig. 2 constitute, together with the secondary winding 52 of transformer II], a partial bridge circuit. Two equal adjacent arms of the bridge are constituted, respectively, by the section of secondary 12 between terminal l6 and mid-tap 22 and by the section between terminal I! and mid-tap 22. The other pair of equal arms are constituted, re-

spectively, by capacitor 32 and resistor 35 in series between secondary terminal Ill and terminal 26 of circuit S2, and capacitor 44 and resistor 43 in series between secondary terminal I6 and terminal 26 of circuit S2. The load circuit from which the undesired oscillations are to be filtered is constituted by cathode-ray tube supply circuit S2, which is connected across the bridge corners constituted by the mid-tap 22 of secondary l2 and the terminal 26 of circuit S2. The filter capacitor 42 and filter capacitor 25, which are in series connection, are connected in shunt with the cathode-ray tube supply circuit S2, between the corner 22 and the corner 26 of the bridge.

In operation of the system illustrated in Fig. 2, the A. C. voltages across filter capacitor 42 of circuit S2 come from two sources,one from the terminal ll of secondary l2 through capacitor 32 and resistor 35, and the other from terminal 16 of secondary l2 through capacitor 44 and resistor 43. These two voltages are in opposition and therefore only,a relatively small ripple voltage remains across filter capacitor 42. Since the remaining ripple to be filtered from circuit S2 is thus small, capacitor 42 need only be small relative to the filter capacitor 34 of Fig. 1 which it replaces. Further by reason of the efficient filtering provided by the above described bridge circuit in Fig. 2 the extra filtering stage constituted by resistor 38 and capacitor 39 of Fig. 1 is eliminated.

In a practical system, the constants for the filter elements in the filter arrangements disclosed in Figs. 1 and 2 for cathode-ray tube supply circuit S2 may be compared as follows:

For the system illustrated in Fig. 1:

Filter capacitor 34 1 mfd. 1500 volts Capacitor 39 1 mfd. 1500 volts Resistor 38 200,000 ohms For the system illustrated in Fig. 2:

Filter capacitor 42 mid. 1500 volts Capacitor 44 .03 mfd.

Resistor 43.... 200,000 ohms It will be readily seen that by reason of the replacing of the filter capacitor 34 of Fig. 1 by the much smaller filter capacitor 42 of Fig. 2 and the elimination of the large capacitor 39 of Fig. 1, a very considerable saving in filter cost. as much as two thirds, is effected by the use of the filtering system, for circuit S2, illustrated in Fig. 2, instead of the filtering system for circuit S2 illustrated in Fig. 1.

My invention has been described herein in particular embodiments for purposes of illustration. It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a current source, a load circuit, means including a rectifier and a transformer having an energizing winding connected to said rectifier to supply power to said circuit from said source, a second load circuit, and means including a rectifier connected in series in said second circuit and across said secondary winding to supply power to said second load circuit from said source, said rectifiers being so arranged and so connected to said winding that the voltage across said second-named rectifier is substantially greater than the voltage across said first-named rectifier.

2. In combination, a current source, a load circuit, a rectifier, a transformer winding, means to supply a voltage to said circuit from said winding through said rectifier, a second load circuit, a second rectifier connected across said winding to supply voltage therefrom to said second circuit, and means to connect said second rectifier in series with said first named circuit, whereby the voltage supplied to said first-named circuit through said first named rectifier is added to the voltage supplied to said second circuit through said second rectifier, said rectifiers being so arranged and so connected to said winding that the voltage across said second-named rectifier is substantially greater than the voltage across said first-named rectifier.

3. In combination, a current source, a load circuit having a filter reactor in series therewith, a rectifier, a transformer winding, means to supply a voltage to said circuit from said winding through said rectifier, a second load circuit, a second rectifier connected to supply voltage therefrom to said second circuit across said winding and means to connect said second rectifier in series with said filter reactor and said first-named circuit whereby the voltage supplied to said second circuit from said winding is the sum of the voltage across the output terminals of said firstnamed circuit, the voltage drop through said reactor, and the voltage supplied to said second circuit through said second rectifier.

4. In combination, a current source, a load circuit, a rectifier, a transformer winding, means to supply a voltage to said circuit from said winding through said rectifier, a second load circuit, a second rectifier connected across said winding and in series in said second circuit to supply rectifier voltage from said winding to said second circuit, a filter capacitor, means to connect said filter capacitor across said second load circuit, and means to impress substantially equal voltages in opposite phase across said filter capacitor from said winding.

5. In combination, a. current source, a load a capacitor and a resistor in series connected between the high tension side of said filter capacitor and one extremity of said winding and a capacitor and a resistor in series connected between said high tension side of said filter capacitor and the other extremity of said winding and having respectively equal capacitance and resistance values with said first named capacitor and resistor in series.

ROBERT B. DOIJE. 

